The present invention relates generally to equipment utilized and operations performed in conjunction with a subterranean well and, in an embodiment described herein, more particularly provides a safety valve with multiple closure devices, or a closure device and a device for enhancing performance of the closure device.
Most safety valve failures are due to leakage past a closure device, such as a flapper or ball closure, of the safety valve. One of the main causes of closure device leakage is damage due to slam closure (i.e., an extremely fast closing of the closure device due, for example, to closing the valve during high velocity gas flow through the valve, etc.). Slam closures can also cause damage to a flow tube or opening prong of the safety valve, and to a pivot for the closure device. Another cause of closure device leakage is erosion due to high velocity flow past sealing surfaces on the closure device and its seat.
Therefore, it will be appreciated that it would be beneficial to reduce the damage due to slam closures and high velocity flow through a safety valve. It is accordingly one of the objects of the present invention to provide such damage reduction. Other objects of the invention are described below.